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Pulsed NMR techniques have been used to study the dynamics of $$^3\hbox {He}$$ confined to the interior of the hexagonal nanochannels of MCM-41 for which the walls were coated with a monolayer of $$^4\hbox {He}$$ as determined by isotherm measurements. The $$^3\hbox {He}$$ was added afterward to form a 1D $$^3\hbox {He}$$ line density of about 0.1 $$\hbox {A}^{-1}$$ , corresponding to a Fermi temperature of $$T_{\mathrm{F}} \sim$$ 120 mK. A distinct and appreciable departure from the Curie law was observed for the nuclear spin magnetization below 0.5 K. The temperature dependence of the nuclear spin–lattice relaxation times, $$T_1$$ , for temperatures $$0.05

MCM-41 is a unique mesoporous material with cylindrical-like pores that provide an ideal platform to study 1D properties of adsorbed atoms (Boninsegni and Moroni in J Low Temp Phys 118(1):1, 2000). In this research, we use pulsed NMR to measure the nuclear spin-lattice relaxation times ( $$T_1$$ ) of $$^3$$ He adsorbed onto $$^4$$ He-preplated MCM-41 over a wide range of temperatures for a line density that would lead to a Fermi temperature of 200 mK. The temperature dependence of the nuclear spin-lattice relaxation time for $$ 0.025

We discuss the analysis of the experimental values of the nuclear spin–lattice and spin–spin relaxation times for the tunneling of $$^3$$ He as isotopic impurities in solid $$^4$$ He. These two relaxation times cannot be described quantitatively using a unique correlation time although it is often presented as such in the literature. In this paper, we discuss how to distinguish the high-frequency portion of the spectral densities that determine the spin–lattice relaxation rates from the low-frequency components which determine the spin–spin relaxation rates.

We present a new simplified derivation of the effect of lattice relaxation that accompanies the quantum tunneling of 3He impurities in solid 4He on the nuclear spin-lattice relaxation of the 3He impurities for very low impurity concentrations. As a result of the larger zero point motion of the 3He impurity compared to the 4He atoms, a significant lattice distortion accompanies the impurity as it moves through the lattice and the dynamics of the impurity depends on both the interaction energy between two 3He atoms and on the relaxation of the lattice for the tunneling impurity. Using a phenomenological model for the lattice relaxation we compare the nuclear spin-lattice relaxation rates observed at low temperatures with the dependence on temperature expected for a 4He lattice relaxation comparable to that observed by Beamish et al. (Phys. Rev. Lett. 96:195304, 2006).

Recent experimental studies of solid 4He indicate a strong correlation between the crystal defects and the onset of a possible supersolid state. We use pulsed NMR techniques to explore the quantum dynamics of the 3He impurities in the solid 4He in order to examine certain theoretical models that describe how the disordered states are related to supersolidity. Because of the very small signal-to-noise ratio at low 3He concentration and the long spin-lattice relaxation time (T 1), it is essential to significantly enhance the NMR sensitivity to be able to carry out the experiments. Here we present the design of a novel low temperature preamplifier which is built with a low noise pseudomorphic HEMT transistor that is embedded into a cross-coil NMR probe. With a low power dissipation of about 0.7 mW, the preamplifier is capable of providing a power gain of 30 dB. By deploying the preamplifier near the NMR coil below 4 K, the noise temperature of the receiver is reduced to approximately 1 K. This preamplifier design also has the potential to be adapted into a low temperature amplifier with both input and output impedance at 50 Ω or a low temperature oscillator.

In fluidized granular matter (such as rapidly flowing sand) heat can flow from colder to hotter granular temperatures, violating Fourier’s law. A simple heuristic explanation for this anomalous heat current is presented, based on the non-equilibrium nature of granular fluids. The heuristic explanation leads to a straightforward calculation of the heat current which is in good agreement with existing, more detailed calculations and with recent experiments.

Nuclear magnetic resonance (NMR) experiments are described for gas-fluidized granular beds, which are important systems for many materials-processing operations. Using pulsed field gradient, magnetic resonance imaging, and hyperpolarized gas NMR, detailed information is obtained for the density and motions of both grains and interstitial gas. In particular, dynamic correlations in the grain density are used to measure the bubble velocity and hyperpolarized xenon gas NMR is used to measure the bubble-emulsion exchange rate. A goal of these measurements is to verify in earth gravity first-principles theories of granular flows.

We report initial NMR studies of gas dynamics in a particle bed fluidized by laser-polarized xenon (129Xe) gas. We have made preliminary measurements of two important characteristics: gas exchange between the bubble and emulsion phases and the gas velocity distribution in the bed. We used T2* contrast to differentiate the bubble and emulsion phases by choosing solid particles with large magnetic susceptibility. Experimental tests demonstrated that this method was successful in eliminating 129Xe magnetization in the emulsion phase, which enabled us to observe the time dependence of the bubble magnetization. By employing the pulsed field gradient method, we also measured the gas velocity distribution within the bed. These results clearly show the onset of bubbling and can be used to deduce information about gas and particle motion in the fluidized bed.

We report initial NMR studies of continuous flow laser-polarized xenon gas, both in unrestricted tubing, and in a model porous media. The study uses Pulsed Gradient Spin Echo-based techniques in the gas-phase, with the aim of obtaining more sophisticated information than just translational self-diffusion coefficients. Pulsed Gradient Echo studies of continuous flow laser-polarized xenon gas in unrestricted tubing indicate clear diffraction minima resulting from a wide distribution of velocities in the flow field. The maximum velocity experienced in the flow can be calculated from this minimum, and is seen to agree with the information from the complete velocity spectrum, or motion propagator, as well as previously published images. The susceptibility of gas flows to parameters such as gas mixture content, and hence viscosity, are observed in experiments aimed at identifying clear structural features from echo attenuation plots of gas flow in porous media. Gas-phase NMR scattering, or position correlation flow-diffraction, previously clearly seen in the echo attenuation data from laser-polarized xenon flowing through a 2 mm glass bead pack is not so clear in experiments using a different gas mixture. A propagator analysis shows most gas in the sample remains close to static, while a small portion moves through a presumably near-unimpeded path at high velocities.

We present vibrating - wire viscosity measurements on a very dilute 3 He -4 He mixture (χ3 = 150 ppm ) in fields up to 14.8 T and temperatures down to 3 mK. The 3 He spin polarization is greater than 99% for the highest field and lowest temperature used. In these conditions, the s-wave scattering rate decreases due to a lack of quasiparticles with the minority spin state. This enhances all transport coefficients including the viscosity. At the lowest temperature, the hydrodynamic damping of the viscometer in a 14.8 T field was more than 10 times larger than in low fields. This indicates a many-fold increase in the mixture viscosity due to spin polarization.

We describe a compact birdcage resonator for low temperature NMR experiments in the frequency range 250–500 MHz. The resonator is completely shielded and thermally isolated from the sample cell, permitting the application of high-power NMR pulses with minimal sample heating. It is fabricated from Kapton-copper laminate using printed-circuit techniques to form the required array of inductive and capacitive elements.

We report new experiments on the transverse and longitudinal spin dynamics of liquid 3 He polarized by an 11.3T field. At the lowest temperatures probed, the transverse spin diffusion coefficient saturates with an apparent anisotropy temperature of Ta=12±2 mK. This temperature dependence is in accord with the general idea of spin-diffusion anisotropy but the value of Ta is half that expected from extrapolating earlier experiments at a lower field. Strong magnetostatic effects in the form of long-lived spin modes are also observed for small gradients and small tipping angles.

We report NMR experiments at 8 T on3He and3He-4He mixtures filling the pores of 95% porous aerogel, for temperatures T ≥ 6 mK. Magnetization measurements of pure3He reveal a localized layer approximately one monolayer thick. The longitudinal relaxation includes a component logarithmic in time, which is apparently associated with a fraction of the localized3He atoms. When the localized3He is displaced by adding4He the logarithmic relaxation disappears and T1for the dominant exponential relaxation increases. Measurements of the spin diffusion coefficient with the aerogel filled with dilute solution in equilibrium with bulk phase-separated mixture provide an unambiguous determination of the spin mean free path,ls = 58 nm

The lattice dynamics of solid He-4 has been explored using pulsed NMR methods to study the motion of He-3 impurities in the temperature range (0.05-0.20 K) where experiments have revealed anomalies attributed to superflow or unexpected viscoelastic properties of the solid He-4 lattice. We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation times that measure the fluctuation spectrum at high and low frequencies, respectively, of the He-3 motion that results from quantum tunneling in the He-4 matrix. The measurements were made for He-3 concentrations 16 < x(3) < 2000 ppm. For He-3 concentrations x(3) = 16 and 24 ppm, large changes are observed for both the spin-lattice relaxation time T-1 and the spin-spin relaxation time T-2 at temperatures close to those for which the anomalies are observed in measurements of torsional oscillator responses and the shear modulus. These changes in the NMR relaxation rates were not observed for higher He-3 concentrations.

We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute 3He in solid 4He in the temperature range 0.01 \leq T \leq 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the 4He lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of 3He impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies., 4 pages, 4 figures

A series of experiments has been carried out on very dilute3He-4He mixtures and on pure3He liquid at very high field/temperature ratios (H≤8 T, T≥4.3mK). In this regime these systems display a strong Leggett-Rice effect, weakly damped paramagnetic spin waves, and significant polarization effects on spin and momentum transport. The dilute mixture experiments used NMR to observe standing spin waves, and vibrating-wire viscometry to measure momentum transport. A very satisfactory agreement is found with the recent kinetic-equation calculations of Jeon and Mullin. The pure3He experiments may provide the first evidence for field-induced relaxation of transverse spin currents.

Transverse spin dynamics have been measured for a very dilute $^{3}\mathrm{\ensuremath{-}}^{4}$He mixture (${\mathit{x}}_{3}$=1.82\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$) polarized by an 8-T magnetic field. The sample was confined to a small spherical resonator, resulting in well-defined spin-wave modes for temperatures below 50 mK. Results are presented for the spin-rotation parameter ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ and spin-wave dispersion ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}$/${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$. It is found that ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{int}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\perp}}}$ increases monotonically as the temperature is decreased below the degeneracy temperature ${\mathit{T}}_{\mathit{F}}$, in apparent disagreement with an earlier experiment.

The viscosity is measured for a Fermi liquid, a dilute $^3$He-$^4$He mixture, under extremely high magnetic field/temperature conditions ($B \leq 14.8$ T, $T \geq 1.5$ mK). The spin splitting energy $\mu B$ is substantially greater than the Fermi energy $k_B T_F$; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for $T \ll T_F$. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a $t$-matrix formalism., Comment: 4 pages, 4 figures

We report experimental studies of the effect of interstitial gas on mass-density-segregation in a vertically-vibrated mixture of equal-sized bronze and glass spheres. Sufficiently strong vibration in the presence of interstitial gas induces vertical segregation into sharply separated bronze and glass layers. We find that the segregated steady state (i.e., bronze or glass layer on top) is a sensitive function of gas pressure and viscosity, as well as vibration frequency and amplitude. In particular, we identify distinct regimes of behavior that characterize the change from bronze-on-top to glass-on-top steady-state., Comment: 4 pages, 5 figures, submitted to PRL; accepted in PRE as rapid communication, with revised text and references

Measurements of the 3He nuclear spin relaxation times of dilute 3He impurities in solid 4He have been used to explore the unusual dynamics of solid 4He at low temperatures. The 3He impurities move through the lattice by quantum mechanical exchange with neighboring 4He atoms. Because of the larger zero point motion of the 3He atoms, there is an appreciable lattice distortion that accompanies the tunneling 3 He atom and the tunneling motion depends on the elastic properties of the 4He lattice. This motion modulates the 3He-3He nuclear dipole- dipole interactions and thus determines the NMR relaxation rates. We compare the observed temperature dependence of the NMR relaxation rates with that expected from the measurements of the shear modulus by Syshchenko et al. [Phys. Rev. Lett. 104, 195301 (2009)].

A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient (PFG) NMR coupled with one-dimensional magnetic resonance imaging (MRI). The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell, 14 pages, 15 figures

A comment is made on the recent PFG NMR measurements by Stallmach, et al. on water-saturated sands [Phys. Rev. Lett. 88, 105505 (2002)]. It is pointed out that the usual law for the time-dependent diffusion coefficient D(t) used by these authors is not valid for a fractal surface. It is shown that (1-D(t)/D0) \~ t^[(3-Ds)/2] at short times for a surface of fractal dimension Ds, where D0 is the bulk diffusion coefficient. Preliminary PFG NMR data on water saturated limestone and plastic beads are presented to illustrate this analysis., 1 page, 1 figure

We have used an NMR technique to measure the short-time, three-dimensional displacement of grains in a system of mustard seeds vibrated vertically at 15g. The technique averages over a time interval in which the grains move ballistically, giving a direct measurement of the granular temperature profile. The dense, lower portion of the sample is well described by a recent hydrodynamic theory for inelastic hard spheres. Near the free upper surface the mean free path is longer than the particle diameter and the hydrodynamic description fails., Comment: 4 pages, 4 figures

Fast NMR imaging was used to measure the density profile of a three-dimensional granular medium fluidized by vertical vibrations of the container. For container acceleration much larger than gravity, the rise in center of mass of the granular medium is found to scale as (v0^alpha)/(N^beta) with alpha = 1.0 +/-0.2 and beta = 0.5 +/- 0.1, where v0 is the vibration velocity and N is the number of grains in the container. This value for alpha is significantly less than found previously for experiments and simulations in one dimension (alpha = 2) and two dimensions (alpha = 1.3-1.5)., Comment: 4 pages, 3 figures

We have measured the 129 Xe spin-lattice relaxation time T 1 for xenon films adsorbed on silica gel in an 8 T magnetic field at dilution refrigerator temperatures, both with and without 3 He filling the sample cell. Without 3 He , T 1 increases rapidly as the temperature is lowered. With 3 He , T 1 is considerably shortened, and is consistent with temperature-independent quantum relaxation. Using this technique, it is possible to brute-force polarize large quantities of xenon in high B / T conditions.

We are conducting an experimental search for spin-diffusion anisotropy in dilute 3 He– 4 He mixtures at very high B / T (17 T, 2 mK). Previous experiments have not reached sufficiently high B / T ratios to observe the effect in very dilute mixtures, for which quantitative theoretical predictions exist. The planned experiments will require NMR experiments at very high values of the dimensionless spin rotation parameter μM . We have performed numerical simulations of the nonlinear spin dynamics to assess the feasibility of spin-wave and spin-echo experiments.

The elementary librational excitations of solid molecular hydrogen are calculated using the recursion method of Haydock. This method permits a correct treatment of the problem of dilution with para-hydrogen. Agreement is obtained with previous calculations of the excitations of pure ortho-hydrogen. It is found that the gap in the single-excitation density of states decreases much faster than the ortho concentration. The specific heat and the NMR line shapes and relaxation times are calculated and compared with experimental data. For ortho concentration less than 0.5, the data suggest the existence of excitations with energies several times smaller than those of the collective librations we consider.

The "recursion method" is applied to the dynamics of disordered lattices, and is used explicitly to calculate properties of isotopically disordered zinc. The specific heat and atomic motion are calculated for the special case of an isotopically pure lattice and compared to previous experimental and theoretical results. Then M\"ossbauer-effect calculations for the high-resolution $^{67}\mathrm{Zn}$ isotope are presented, including evaluations of the M\"ossbauer line shift with temperature, the anisotropic recoil-free fraction, and the Goldanskii-Karyagin effect. In addition, the effect of zero-point motion on the M\"ossbauer line position and linewidth in isotopically disordered zinc is discussed.

We have observed the deuteron NMR absorption line at 46 MHz in phase III of the partially deuterated methanes in the temperature range 40 mK to 4 K. For CH${\mathrm{D}}_{3}$ the line shape depends strongly on the temperature up to 700 mK. A model is developed for the tunneling states of CH${\mathrm{D}}_{3}$ which reproduces both the derivative NMR line shape and the temperature dependence of the line area. We find that the line shape is determined by the interaction of the deuteron quadrupole moment with the gradient of the electric field of the molecular carbon-deuteron bond. The coupling constant for this interaction, $\frac{{e}^{2}\mathrm{qQ}}{h}$, is measured to be 158\ifmmode\pm\else\textpm\fi{}8 kHz, and the broadening of the NMR line is found to be consistent with the strength of the intramolecular dipole-dipole interactions. The data imply an absence of spin-species conversion in CH${\mathrm{D}}_{3}$ on a time scale of 10 h. Our tunneling-level model for CH${\mathrm{D}}_{3}$ is also compared with thermodynamic measurements. For C${\mathrm{H}}_{2}$${\mathrm{D}}_{2}$ in the temperature range 40 to 60 mK, the NMR line is compared with the predictions of an energy-level scheme deduced from neutron scattering and thermodynamic measurements. We conclude that the tunneling of the deuterons around the ${C}_{3}$ symmetry axis in CH${\mathrm{D}}_{3}$, and around the ${C}_{2}$ symmetry axis in C${\mathrm{H}}_{2}$${\mathrm{D}}_{2}$, proceeds at a rate fast compared with $\frac{{e}^{2}\mathrm{qQ}}{\ensuremath{\hbar}}$. No absorption lines of satisfactory signal-to-noise ratio were observed for C${\mathrm{H}}_{3}$D.

We present measurements of nuclear spin-lattice relaxation in solid ${\mathrm{D}}_{2}$ for para concentrations $0.24lXl0.31$ and temperatures $40lTl700$ mK. No evidence is seen for a well-defined transition into the quadrupolar glass state. A model of para-ortho cross relaxation is presented which allows our ${\mathrm{D}}_{2}$ data to be compared with previous ${\mathrm{H}}_{2}$ relaxation data.

By monitoring the time dependence of the nuclear magnetic susceptibility we have measured the spin-species conversion rate in solid C${\mathrm{H}}_{4}$ for temperatures of 4-23 K. We discuss the relation to previous measurements and to the available theory of spin-species conversion.

It is proposed that the low-lying excitations of solid hydrogen in the quadrupolar glass state may be described in terms of a distribution of “effective spin-one quadrupoles”. This model provides a qualitative explanation for the temperature dependence of NMR lineshapes, and of the low temperature specific heat.

An estimate is presented for the temperature difference between a sample of solid hydrogen and its container, based on the known thermal boundary resistance and the heat load due to ortho-para conversion. NMR Curie-Law thermometry is used to measure the true temperature of hydrogen cooled by a dilution refrigerator.